Thin-film magnetic head

ABSTRACT

A thin-film magnetic head including a ring-shaped magnetic core and a coil surrounded by the magnetic core, given that an inner circumferential length of the magnetic core surrounding the coil is Lc, a magnetic gap length is g, a magnetic gap depth is D, an average magnetic flux density (unit: T (tesla)) is Bav and an effective magnetic permeability of the magnetic core is mu, wherein Lc, g and D are determined in such a manner that a magnetomotive force I needed for recording, expressed by a following equation (1), becomes equal to or less than 0.1 A.T (Ampere.Turn):where Log is anatural logarithm, and variables in the equation (1) are expressed in SI units.

This application is a Division of application Ser. No. 09/195,107, filedon Nov. 18,1998, now abandoned, which is a Division of application Ser.No. 08/901,667, filed Jul. 28, 1997, abandoned, which is a File WrapperContinuation of U.S. Ser. No. 08/212,866, filed Mar. 15,1994, abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a thin-film magnetic head for use in amagnetic disk apparatus, a VTR, etc., and a magnetic write/readapparatus equipped with this magnetic head, and more particularly, to avery small thin-film magnetic head which has low recording magnetomotiveforce necessary for magnetizing a magnetic recording medium, has a fewernumber of recording coil turns and has a very narrow track width, and amagnetic write/read apparatus equipped with this magnetic head.

2. Description of the Related Art

For an inductive magnetic head which has been conventionally popular,when used both for writing and reading, it is in principle advantageousto increase the number of coil turns because this provides a largerreading output. With such a magnetic head used exclusively forinformation writing, however, the number of-coil turns can be reduced aslong as the magnetomotive force required for writing is satisfied. Theinductive magnetic head for exclusive use in information writing,therefore, has a simpler structure than the aforementioned inductivemagnetic head designed both for writing and reading, thus facilitatingthe head fabrication process and improving the production yield. Themagnetic head for writing only has a further advantage in easierminiaturization of the magnetic core portion and easily ensuring thehigh efficiency of the head.

It is a magnetic head with a single-turn coil which has the simpleststructure and is attractive. It is known that the recording currentneeded to magnetize a magnetic recording medium using a single-turnmagnetic head fabricated by the prior art design technology is around 1A (Ampere), namely, 0.7 to 0.8 A or 1.5 A. (See E. P. Valsyn and L. F.Shew, “Performance of Single-Turn Film Heads,” IEEE Trans. MAG-9, No. 3,Sep. 1973, and W. Chynoweth, “Small Thin-film Transducers Point to Fast,Dense Storage Systems, Electronics, July 25, pp. 122-127, 1974.)

This means that the magnetomotive force of the conventional single-turncoil magnetic head does not differ from that of the conventionalinductive magnetic head designed for writing and reading (several dozensof turns), which is about 1 A·T (Ampere·Turn).

Since the conventional single-turn head or few-turns head requires arecording current larger by a factor of several tens than that of thewriting/reading head, the burden on the driver circuit to supply therecording current is very heavy. What is more, because of the largecurrent, the heat generated by the coil portion will deteriorate thecharacteristic and reliability of the head. To cope with never stoppingimprovement of the density of magnetic recording apparatuses, there willbe expected demands for further miniaturization of the magnetic core andfurther reduction of the number of coil turns. This therefore requiressome design scheme for a low-magnetomotive force magnetic head, whichcan magnetize a magnetic recording medium with a low magnetomotiveforce, preferably of several dozens of milliamperes·turns (mA·T),similar to the writing current needed by the conventional inductivewrite/read magnetic head.

Further, since the thickness of the magnetic pole in the plane facingthe recording medium for the conventional inductive magnetic head is onthe order of several micrometers (μm), the dimensional tolerance ofmachining for the pole track width has been considered to be limited toaround ±0.5 μm as long as the state-of-the-art film etching process isused, and it is very difficult to provide a narrow track width of 1 μmor below. A solution to this shortcoming has been craved so far.

SUMMARY OF THE INVENTION

It is therefore a primary object of the present invention to provide avery small, single-turn or few-turns thin-film magnetic head, whichneeds considerably lower magnetomotive force for recording than theconventional heads, is excellent in processing precision, and willensure recording with a very narrow track width of several μm ornarrower, particularly, 1 μm or narrower.

It is another object of this invention to provide a magnetic write/readapparatus which will exhibit excellent writing and readingcharacteristics and a high reading S/N ratio.

To achieve the above objects, according to one aspect of this invention,there is provided a thin-film magnetic head comprising a ring-shapedmagnetic core and a coil surrounded by the magnetic core, given that aninner circumferential length of the magnetic core surrounding the coilis Lc, a magnetic gap length is g, a magnetic gap depth is D, an averagemagnetic flux density (unit: T (tesla)) is Bav and an effective magneticpermeability of the magnetic core is μ, Lc, g and D being determined insuch a manner that a magnetomotive force I needed for recording,expressed by a following equation (1), becomes 0.001 A·T to 0.1 A·T(Ampere·Turn): $\begin{matrix}{I = \frac{2\pi \quad {DBav}}{{\mu Log}\{ {\lbrack {( {{Lc} + g} ) + {2\pi \quad D}} \rbrack/( {{Lc} + g} )} \}}} & \text{(1)}\end{matrix}$

wherein Log is a natural logarithm, and variables in the equation (1)are expressed in SI units.

According to another aspect of this invention, there is provided aperpendicular thin-film magnetic head comprising a magnetic core havinga main magnetic pole and a return path of a high magnetic permeabilityto be magnetically coupled to the main magnetic pole, and a coilsurrounded by the magnetic core, for accomplishing writing and readingwhen in use with a perpendicular double-layered magnetic recordingmedium having a highly permeable layer and a perpendicular recordinglayer laminated on a substrate in a named order, given that an innercircumferential length of the magnetic core surrounding the coil is Lc,a distance from the medium opposing face of the perpendicular thin-filmmagnetic head to a recording-layer side face of the highly permeablelayer of the recording medium is S, an interval between the mainmagnetic pole and the return path at a position of the medium opposingface is Lb, a film thickness in a vicinity of the medium opposing faceof the main magnetic pole is Tm, an average value of the density of amagnetic flux (unit: T (tesla)) generated toward the highly permeablelayer from a distal end portion of the main magnetic pole, needed forsufficiently magnetizing the perpendicular recording layer, is Bav andan effective magnetic permeability of the magnetic core is μ, Lc, S. Lband Tm being determined in such a manner that a magnetomotive force Ineeded for recording, expressed by a following equation (2), becomes0.001 A·T to 0.1 A·T: $\begin{matrix}{I = \frac{2\pi \quad {TmBav}}{{\mu Log}\{ {( {L + {2\pi \quad {Tm}}} )/L} \}}} & \text{(2)}\end{matrix}$

wherein Log is a natural logarithm, L=Lc+2S+Lb, and variables in theequation (2) are expressed in SI and variables in the equation (2) areexpressed in SI units.

According to a further aspect of this invention, there is provided amagnetic writing/reading apparatus equipped with a recording magnetichead comprising a ring-shaped magnetic core and a coil surrounded by themagnetic core, and a magnetic recording medium on which recording isdone by the recording magnetic head, given that an inner circumferentiallength of the magnetic core surrounding the coil of the recordingmagnetic head is Lc, a magnetic gap length is g, a magnetic gap depth isD, an average magnetic flux density (unit: T (tesla)) is Bav and aneffective magnetic permeability of the magnetic core is μ, Lc, g and Dare determined in such a manner that a magnetomotive force I needed forrecording, expressed by a following equation (1), becomes 0.001 A·T to0.1 A·T (Ampere·Turn), and a magnetic field Hx in a magnetic-headrunning direction of the magnetic recording medium immediately below acenter portion of a magnetic gap of the recording magnetic head beingexpressed by a following equation (3) and the magnetic field Hx andcoercive force Hc of the magnetic recording medium having a relation ofHx>Hc: $\begin{matrix}{I = \frac{2\pi \quad {DBav}}{{\mu Log}\{ {\lbrack {( {{Lc} + g} ) + {2\pi \quad D}} \rbrack/( {{Lc} + g} )} \}}} & \text{(1)}\end{matrix}$

where Log is a natural logarithm, and variables in the equation (1) areexpressed in SI units, and $\begin{matrix}{{Hx} = {\frac{2{Bs}}{{\pi\mu}_{0}}\lbrack {{\tan^{- 1}\frac{t_{w}( {D + d + \delta} )}{( {g\sqrt{( {t_{w}/2} )^{2} + ( {d + \delta} )^{2} + ( {g/2} )^{2}}} )}} - {\tan^{- 1}\frac{t_{w}( {d + \delta} )}{( {g\sqrt{( {t_{w}/2} )^{2} + ( {d + \delta} )^{2} + ( {g/2} )^{2}}} )}}} \rbrack}} & (3)\end{matrix}$

where g is a magnetic gap length of the recording magnetic head, D is amagnetic gap depth of the recording magnetic head, t_(w) is a trackwidth, Bs is a saturation magnetic flux density (unit: T (tesla)) of amagnetic head core necessary to generate a recording magnetic fieldneeded for magnetization of the magnetic recording medium, μ₀ is amagnetic permeability in vacuum, d is spacing between the recordingmagnetic head and the magnetic recording medium, and δ is a thickness ofa recording layer of the magnetic recording medium.

According to a still further aspect of this invention, there is provideda magnetic write/read apparatus equipped with a recording magnetic headcomprising a magnetic core having a main magnetic pole and a return pathof a high magnetic permeability to be magnetically coupled to the mainmagnetic pole, and a coil surrounded by the magnetic core, and a readingmagnetic head provided integrally with or separate from the recordingmagnetic head, for accomplishing writing and reading when in use with aperpendicular double-layered magnetic recording medium having a highlypermeable layer and a perpendicular recording layer laminated on asubstrate in a named order, given that an inner circumferential lengthof the magnetic core surrounding the coil of the recording magnetic headis Lc, a distance from the medium opposing face of the recordingmagnetic head to a recording-layer side face of the highly permeablelayer of the recording medium is S, an interval between the mainmagnetic pole and the return path at a position of the medium opposingface is Lb, a film thickness in a vicinity of the medium opposing faceof the main magnetic pole is Tm, an average value of the density of amagnetic flux (unit: T (tesla)) generated toward the highly permeablelayer from a distal end portion of the main magnetic pole, needed forsufficiently magnetizing the perpendicular recording layer, is Bav andan effective magnetic permeability of the magnetic core is μ, Lc, S, Lband Tm being determined in such a manner that a magnetomotive force Ineeded for recording, expressed by a following equation (2), becomes0.001 A·T to 0.1 A·T, and a magnetic field Hy in a directionperpendicular to-a main surface of the magnetic recording mediumimmediately below the main magnetic pole of the recording magnetic headbeing expressed by a following equation (4) and the magnetic field Hyand coercive force Hc of the magnetic recording medium having a relationof Hy>Hc: $\begin{matrix}{I = \frac{2\pi \quad {TmBav}}{{\mu Log}\{ {( {L + {2\pi \quad {Tm}}} )/L} \}}} & \text{(2)}\end{matrix}$

wherein Log is a natural logarithm, L=Lc+2S+Lb, and variables in theequation (2) are expressed in SI units, and $\begin{matrix}{{Hy} = {\frac{2{Bs}}{{\pi\mu}_{0}}\tan^{- 1}{t_{w} \cdot \frac{t_{m}}{4( {d + \delta} )\sqrt{( {t_{w}/2} )^{2} + ( {t_{m}/2} )^{2} + ( {d + \delta} )^{2}}}}}} & (4)\end{matrix}$

where tm is a thickness of the main magnetic pole of the recordingmagnetic head, t_(w) is a track width, Bs is a saturation magnetic fluxdensity (unit: T (tesla)) of the main magnetic pole necessary togenerate a recording magnetic field needed for magnetizing the magneticrecording medium, μ₀ is a magnetic permeability in vacuum, d is spacingbetween the recording magnetic head and the magnetic recording medium,and δ is a thickness of a recording layer of the magnetic recordingmedium.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a diagram schematically showing a magnetic head for explainingthe action of this invention;

FIG. 2 is a graph showing the relation between at magnetomotive forceand the inner circumferential length of a magnetic core for explainingthe action of this invention;

FIG. 3 is a cross-sectional view showing a ring-shaped horizontalthin-film magnetic head according to a first embodiment of thisinvention;

FIG. 4 is a cross-sectional view showing a ring-shaped thin-filmmagnetic head according to a second embodiment of this invention;

FIG. 5 is a cross-sectional view showing a perpendicular thin-filmmagnetic head according to a third embodiment of this invention;

FIG. 6 is a cross-sectional view showing a perpendicular thin-filmmagnetic head according to a fourth embodiment of this invention;

FIG. 7 is a cross-sectional view showing a ring-shaped horizontalthin-film magnetic head according to a fifth embodiment of thisinvention;

FIG. 8 is a cross-sectional view showing a ring-shaped thin-filmmagnetic head according to a sixth embodiment of this invention;

FIG. 9 is a cross-sectional view showing a perpendicular thin-filmmagnetic head according to a seventh embodiment of this invention;

FIG. 10 is a cross-sectional view showing a perpendicular thin-filmmagnetic head according to an eighth embodiment of this invention;

FIGS. 11A to 11C are cross-sectional views of a magnetic head showingwhere an antiferromagnetic film is located;

FIG. 12 is a view showing a magnetic write/read apparatus according to aninth embodiment of this invention; and

FIG. 13 is a view showing a magnetic/read apparatus according to a tenthembodiment of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The first aspect of this invention provides a thin-film magnetic headcomprising a ring-shaped magnetic core and a coil surrounded by themagnetic core.

This thin-film magnetic head is characterized in that, given that aninner circumferential length of the magnetic core surrounding the coilis Lc, a magnetic gap length is g, a magnetic gap depth is D, an averagemagnetic flux density (unit: T (tesla)) is Bav and an effective magneticpermeability of the magnetic core is μ, Lc, g and D are determined insuch a manner that a magnetomotive force I needed for writing, expressedby a following equation (1), becomes equal to or less than 0.1 A·T(Ampere·Turn): $\begin{matrix}{I = \frac{2\pi \quad {DBav}}{{\mu Log}\{  \lbrack {( {L + {2\pi \quad D}} )/L}  \} }} & \text{(1)}\end{matrix}$

wherein Log is a natural logarithm, L=Lc+g, and variables in theequation (1) are expressed in SI units.

It is preferable that the magnetomotive force I range from 0.001 A·T to0.07 A·T, more preferably, from 0.01 A·T to 0.07 A·T. Further, it ispreferable that D is in a range from 0.1 to 0.5 μm.

In this thin-film magnetic head, the magnetic core may comprise a firstmagnetic layer formed on a head substrate and a second magnetic layerformed on the first magnetic layer. In this case, a thin film or amulti-layered thin-film, which is made of at least one type of magneticor non-magnetic material selected from a group of a non-magneticmaterial, a magnetic material having a lower saturation magnetic fluxdensity than that of the magnetic core and an antiferromagneticmaterial, may be provided at the interface between the first magneticlayer and the second magnetic layer.

The non-magnetic material incudes Al₂O₃, SiO₂ and Cu, the magneticmaterial having a lower saturation magnetic flux density than that ofthe magnetic core includes CoZr-based amorphous material and Parmalloycontaining Nb or Rh, and the antiferromagnetic material includes FeMn,NiO and PtMn.

This invention can also be adapted for a perpendicular thin-filmmagnetic head.

The second aspect of this invention provides a perpendicular thin-filmmagnetic head comprising a magnetic core having a main magnetic pole anda return path of a high magnetic permeability to be magnetically coupledto the main magnetic pole, and a coil surrounded by the magnetic core,for accomplishing writing and reading when in use with a perpendiculardouble-layered magnetic recording medium having a highly permeable layerand a perpendicular recording layer laminated on a substrate in a namedorder.

This perpendicular thin-film magnetic head is characterized in that,given that an inner circumferential length of the magnetic coresurrounding the coil is Lc, a distance from a medium opposing face ofthe perpendicular thin-film magnetic head to a recording-layer side faceof the highly permeable layer of the recording medium is S, an intervalbetween the main magnetic pole and the return path at a position of themedium opposing face is Lb, a film thickness in a vicinity of the mediumopposing face of the main magnetic pole is Tm, an average value of thedensity of a magnetic flux (unit: T (tesla)) generated toward the highlypermeable layer from a distal end portion of the main magnetic pole,needed for sufficiently magnetizing the perpendicular recording layer,is Bav and an effective magnetic permeability of the magnetic core is μ,Lc, S, Lb and Tm being determined in such a manner that a magnetomotiveforce I needed for recording, expressed by a following equation (2),becomes 0.001 A·T to 0.1 A·T: $\begin{matrix}{I = \frac{2\pi \quad {TmBav}}{{\mu Log}\{ {( {L + {2\pi \quad {Tm}}} )/L} \}}} & \text{(2)}\end{matrix}$

where Log is a natural logarithm, L=Lc+2S+Lb, and variables in theequation (2) are expressed in SI units.

It is preferable in this perpendicular thin-film magnetic head too thatthe magnetomotive force I range from 0.001 A·T to 0.07 A·T, morepreferably, from 0.01 A·T to 0.07 A·T. Further, it is preferable that Dis in a range from 0.1 to 0.5 μm.

In this perpendicular thin-film magnetic head, a thin-film or amulti-layered thin-film, made of at least one type of magnetic ornon-magnetic material selected from the group consisting of anon-magnetic material, a magnetic material having a lower saturationmagnetic flux density than those of the main magnetic pole and thereturn path, and an antiferromagnetic material, may be provided at theinterface between the main magnetic pole and the return path.

According to the thin-film magnetic heads of this invention with theabove-described structures, it is possible to magnetize a magneticrecording medium with magnetomotive force significantly lower than thatof the conventional ring-shaped inductive magnetic head, thusfacilitating the reduction of the number of turns of the coil and theminiaturization of the magnetic core with high reliability. Further, thefabrication of the magnetic heads become easier and the production yieldis improved. It is also possible to accomplish high working precision toform a magnetic core with a narrow track width of several μm or below.

The third aspect of this invention provides a magnetic write/readapparatus equipped with a writing magnetic head comprising a ring-shapedmagnetic core and a coil surrounded by the magnetic core, and a magneticrecording medium on which recording is done by the recording magnetichead.

This magnetic write/read apparatus is characterized in that, given thatan inner circumferential length of the magnetic core surrounding thecoil of the recording magnetic head is Lc, a magnetic gap length is g, amagnetic gap depth is D, an average magnetic flux density (unit: T(tesla)) is Bav and an effective magnetic permeability of the magneticcore is μ, Lc, g and D are determined in such a manner that amagnetomotive force I needed for recording, expressed by the aboveequation (1), becomes 0.001 A·T to 0.1 A·T (Ampere·Turn), and a magneticfield Hx in a magnetic-head running direction of the magnetic recordingmedium immediately below a center portion of the recording magnetic headbeing expressed by a following equation (3) and the magnetic field Hxand coercive force Hc of the magnetic recording medium having a relationof Hx>Hc: $\begin{matrix}{{{{{Hx} = \frac{2{Bs}}{{\pi\mu}_{0}}}}\tan^{- 1}\frac{t_{w}( {D + d + \delta} )}{g\sqrt{( {t_{w}/2} )^{2} + ( {d + \delta} )^{2} + ( {g/2} )^{2}}}} - {\tan^{- 1}\frac{t_{w}( {d + \delta} )}{g\sqrt{( {t_{w}/2} )^{2} + ( {d + \delta} )^{2} + ( {g/2} )^{2}}}}} & (3)\end{matrix}$

wherein g is a magnetic gap length of the recording magnetic head, D isa magnetic gap depth of the recording magnetic head, t_(w) is a trackwidth, Bs is a saturation magnetic flux density (unit: T (tesla)) of amagnetic head core necessary to generate a recording magnetic fieldneeded for magnetization of the magnetic recording medium, po is amagnetic permeability in vacuum, d is spacing between the recordingmagnetic head and the magnetic recording medium, and 6 is a thickness ofa recording layer of the magnetic recording medium, and whereinvariables in the equation (3) are expressed in SI units.

It is preferable that the magnetomotive force I range from 0.001 A·T to0.07 A·T, more preferably, from 0.01 A·T to 0.07 A·T. It is preferablethat D be in a range from 0.1 to 0.5 μm.

In this magnetic write/read apparatus, the magnetic core may comprise afirst magnetic layer formed on a head substrate and a second magneticlayer formed on the first magnetic layer. In this case, a thin film or amulti-layer thin-film, made of at least one type of magnetic ornon-magnetic material selected from a group of a non-magnetic material,a magnetic material having a lower saturation magnetic flux density thanthat of the magnetic core and an antiferromagnetic material, may beprovided at the interface between the first magnetic layer and thesecond magnetic layer.

The above-mentioned material can be used as the material for the thinfilm.

The fourth aspect of this invention provides a magnetic write/readapparatus equipped with a recording magnetic head comprising a magneticcore having a main magnetic pole and a return path of a high magneticpermeability to be magnetically coupled to the main magnetic pole, and acoil surrounded by the magnetic core, and a reading magnetic headprovided integrally with or separate from the recording magnetic head,for accomplishing writing and reading when in use with a perpendiculardouble-layered magnetic recording medium having a highly permeable layerand a perpendicular recording layer laminated on a substrate in a namedorder.

This magnetic write/read apparatus is characterized in that, given thatan inner circumferential length of the magnetic core surrounding thecoil of the writing magnetic head is Lc, a distance from a mediumopposing face of the recording magnetic head to a recording-layer sideface of the highly permeable layer of the recording medium is S, aninterval between the main magnetic pole and the return path at aposition of the medium opposing face is Lb, a film thickness in avicinity of the medium opposing face of the main magnetic pole is Tm, anaverage value of the density of a magnetic flux (unit: T (tesla))generated toward the highly permeable layer from a distal end portion ofthe main magnetic pole, needed for sufficiently magnetizing theperpendicular recording layer, is Bav and an effective magneticpermeability of the magnetic core is μ, Lc, S, Lb and Tm beingdetermined in such a manner that a magnetomotive force I needed forwriting, expressed by the above equation (2), becomes 0.001 A·T to 0.1A·T, and a magnetic field intensity Hy in a direction perpendicular to asurface of the magnetic recording medium immediately below the mainmagnetic pole of the writing magnetic head being expressed by afollowing equation (4) and the magnetic field Hy and coercive force Hcof the magnetic recording medium having a relation of Hy>Hc:$\begin{matrix}{{Hx} = {{\frac{2{Bs}}{{\pi\mu}_{0}} \cdot \tan^{- 1}}\quad \frac{t_{w} \cdot t_{m}}{4( {d + \delta} )\sqrt{( {t_{w}/2} )^{2} + ( {t_{m}/2} )^{2} + ( {d + \delta} )^{2}}}}} & (4)\end{matrix}$

wherein tm is a thickness of the main magnetic pole of the recordingmagnetic head, t_(w) is a track width, Bs is a saturation magnetic fluxdensity (unit: T (tesla)) of the main magnetic pole necessary togenerate a recording magnetic field needed for magnetizing the magneticrecording medium, μ₀ is a magnetic permeability in vacuum, d is spacingbetween the recording magnetic head and the magnetic recording medium,and 6 is a thickness of a recording layer of the magnetic recordingmedium, and wherein variables in the equation (4) are expressed in SIunits.

In this perpendicular thin-film magnetic head, a thin film or amulti-layered thin-film, made of at least one type of magnetic ornon-magnetic material selected from a group of a non-magnetic material,a magnetic material having a lower saturation magnetic flux density thanthose of the main magnetic pole and the return path, and anantiferromagnetic material, may be provided at the interface between themain magnetic pole and the return path.

The function of this invention will now be explained on the basis of thedesign scheme, developed by the present inventors, for a very smallthin-film magnetic head with low magnetomotive force and high workingprecision.

Let us consider a coil having a circular cross section a cylindricalmagnetic core that concentrically surrounds this coil, as shown inFIG. 1. A very narrow magnetic gap is formed in this magnetic core.Given that the inner radius of the magnetic core is Rin, the outerradius of the magnetic core is Rout (from which the thickness of themagnetic core is ΔR=Rout−Rin), the magnetic gap length is g, the trackwidth of the magnetic core is W, the total magnitude of the recordingcurrent that flows across the coil is I (equivalent to magnetomotiveforce), and the effective magnetic permeability of the magnetic core isμ, the density of a magnetic flux Φ induced on the magnetic core by thecurrent I is expressed by an equation (5) below in approximation.$\begin{matrix}\begin{matrix}{\Phi = {W{\int_{Rin}^{Rout}{\frac{\mu \quad I}{2\quad \pi \quad R}\quad {R}}}}} \\{= {\frac{\mu \quad {WI}}{2\pi}{{Log}( {{Rout}/{Rin}} )}}}\end{matrix} & \text{(5)}\end{matrix}$

Thus, an average value Bav of the density of a magnetic flux, induced onthe magnetic core by the current I, in the thickness wise direction(radius direction in FIG. 1) of the magnetic core is expressed by thefollowing equation (6); the average value Bav is nearly the same as theaverage magnetic flux density in the magnetic gap. In the equation (6),“Log” is a natural logarithm. $\begin{matrix}{{Bav} = {\frac{\mu \quad I}{2{\pi ( {{Rout} - {Rin}} )}}{{Log}( {{Rout}/{Rin}} )}}} & \text{(6)}\end{matrix}$

Rewriting the equation (6) yields: $\begin{matrix}{I = \frac{2{\pi ( {{Rout} - {Rin}} )}{Bav}}{{\mu Log}( {{Rout}/{Rin}} )}} & \text{(7)}\end{matrix}$

Let us consider a simple case where Rout and Rin are made smaller withRout/Rin being a constant. It is understood from the equation (7) thatwith μ being a constant, the magnetomotive force I necessary to obtain aconstant Bav decreases in proportion to (Rout−Rin). This means thatmaking the magnetic core of the magnetic head properly compact willsignificantly reduce the recording magnetomotive force.

It is to be emphasized that since the above-described design scheme hasnot been employed in fabricating the conventional inductive magneticheads, regardless of bulk heads or thin-film heads, magnetomotive forceof above several hundred mA·T (about 1 A·T on an average) is neededconventionally.

FIG. 2 shows the result of computing the relation between themagnetomotive force I necessary for obtaining Bav=1T and the innercircumferential length Lc (=2 π Rin: the magnetic gap length gdisregarded) of the magnetic core as an example, with α=Rout/Rin and ptaken as parameters, using the equation (7). The value of (Rout−Rin) isobtained by (α−1)Lc/(2π).

Referring to FIG. 2, for α=1.1 for μ=200 (value as the specific magneticpermeability), if Lc is reduced to 5 μm from 1000 μm, the magnetomotiveforce I is decreased by a factor of 200 to about 20 mA·T from about 4A·T. This value, about 20 mA·T, is nearly equal to or smaller than therecording current value needed to magnetize the magnetic recordingmedium using an ordinary write/read inductive magnetic head with manyturns coil. It is to be noted that the values of (Rout−Rin) respectivelycorresponding to Lc=1000 μm and Lc=5 μm are 15.9 μm and 0.08 μm.

Even if the value of μ (specific magnetic permeability) obtained forLc=5 μm is just “50” for some reason, it is apparent that recording canbe done with low magnetomotive force that is a quarter of that in thecase of the mentioned Lc=1000 μm, i.e., about 80 mA·T. Apparently, theuse of the design scheme expressed in the equation (5) for a smallthin-film magnetic head will provide a thin-film magnetic head withconsiderably low magnetomotive force.

The working precision on the pole track width on the medium opposingface is very important in fabricating a magnetic head. Generallyspeaking, the dimensional tolerance of machining for the pole trackwidth should be set to {fraction (1/10)} of a predetermined track widthor less. According to the state-of-the-art thin-film head fabricatingprocess, the dimensional tolerance for the track width of about 5 μm andthe magnetic core thickness of 3 to 4 μm is about ±0.5 μm, which almostsatisfies the above condition. If the existing semiconductor processtechnology is adapted properly, the dimensional tolerance for the trackwidth can be reduced approximately by a factor of 10 by reducing themagnetic core thickness by a factor of 10.

To achieve a very narrow track width of 1 μm or narrower, therefore, thedimensional tolerance for the pole track width should be set as large as±0.1 μm or smaller, or the magnetic core thickness at least on themedium opposing face should be set to or below 1 μm. In the case offabricating a separate write/read type thin-film magnetic head having alamination structure of a recording head and a reading head like amagneto resistive head, the accuracy of positioning the recording headand the reading head as well as the dimensional tolerance for the poletrack width are very concerning matters. In this type of recording head,therefore, sufficient write/read characteristics and reading SIN ratioshould be attained even in consideration of the dimensional tolerancefor the pole track width, the positioning dimensional tolerance, anoff-track amount, and so forth in order to achieve a track width of 1 μmor narrower.

It is generally necessary to set the effective sum of those dimensionaltolerances or errors to {fraction (1/10)} of the recording track width.This requires that the dimensional tolerance for the pole track width besuppressed down to or below {fraction (1/10)} of the recording trackwidth. More specifically, for a track width of 1 μm or narrower, it ispreferable that the dimensional tolerance for the pole track widthshould be set to ±0.05 μm or smaller, or the magnetic core thickness onthe medium opposing face should be set to or below 0.5 μm. In theaforementioned example (Lc=5 μm), since the magnetic core thickness is0.08μ, the dimensional tolerance for the track width is {fraction(1/10)} thereof, thus ensuring a very narrow track of 1 μm or narrower.It is now apparent that the use of the new design scheme expressed bythe equation (7) will provide a thin-film magnetic head with a verynarrow track width of 1 μm or narrower.

There will now be described a write/read apparatus for accomplishingwriting and reading an information using the thin film magnetic headdescribed above.

FIG. 12 shows a write/read apparatus equipped with a ring-shaped thinfilm magnetic head 21, and FIG. 13 shows a write/read apparatus equippedwith a perpendicular thin film magnetic head 22. In FIGS. 12 and 13, adimension of every part of the apparatus is shown. The dimensions areparameters for reading the information written in a recording layer 32of a magnetic recording medium 31 running under the thin film magnetichead 21, 22.

In the magnetic write/read apparatus equipped with the ring-shaped head21 and shown in FIG. 12, the intensity Hx of the magnetic field in therunning direction of the magnetic head immediately below the centralportion of a magnetic gap of the writing magnetic head is induced asfollows:

Where Bs is a saturation magnetic flux density of the magnetic core ofthe magnetic head, the maximum value Hx of the writing magnetic fieldintensity in the running direction of the recording truck at point P onthe bottom surface of the magnetic recording layer immediately below themagnetic gap, is expressed by an equation (8) below. $\begin{matrix}{{Hx} = {\frac{2 \cdot {Bs}}{{\pi\mu}_{0}}\{ {{\tan^{- 1}\quad \frac{{tw} \times ( {D + d + \delta} )}{g \times \sqrt{\frac{{tw}^{2}}{2} + ( {d + \delta} )^{2} + \frac{g^{2}}{2}}}} - \tan - {1\quad \frac{{tw} \times ( {d + \delta} )}{g\sqrt{\frac{{tw}^{2}}{2} + ( {d + \delta} )^{2} + \frac{g^{2}}{2}}}}} \}}} & (8)\end{matrix}$

tw: track width of magnetic head

g: magnetic gap

d: spacing between head and medium

δ: thickness of magnetic recording layer

In the magnetic write/read apparatus equipped with the perpendicularhead 22 and shown in FIG. 13, the intensity Hy of the magnetic field ina direction perpendicular to a surface of the magnetic recording medium31 immediately below the central portion of the recording magnetic pole22 is induced as follows:

Where Bs is a saturation magnetic flux density of the main magneticpole, and considering an effect due to the mirror image 23 of the mainmagnetic pole, cause by the highly permeable layer 33, the maximum valueHy of the writing magnetic field intensity in a direction perpendicularto a surface of the magnetic recording medium at point P (x=0, y=d+δ,z=0) on the bottom surface of the perpendicular recording layer 32immediately below the main magnetic pole is expressed by an equation (9)below. $\begin{matrix}{{Hy} = {\frac{2 \cdot {Bs}}{{\pi\mu}_{0}} \times \tan^{- 1}\quad \frac{{tw} \times {tm}}{4( {d + \delta} ) \times \sqrt{\frac{{tw}^{2}}{2} + \frac{{tm}^{2}}{2} + ( {d + \delta} )^{2}}}}} & \text{(9)}\end{matrix}$

tw: track width of main magnetic pole

tm: thickness of main magnetic pole

d: spacing between main magnetic pole and recording layer

δ: thickness of perpendicular recording layer

Various embodiments of this invention will now be described referring tothe accompanying drawings.

Embodiment 1

FIG. 3 is a cross section showing a thin-film magnetic head according tothe first embodiment of this invention. This thin-film magnetic head isa ring-shaped horizontal (planar) type thin-film magnetic head, whichcomprises a magnetic layer 1 a, an insulating layer 3, a coil 4, amagnetic layer 2 a, a magnetic layer 2 b and a head protective layer 5laminated in order on a head substrate 6, with a magnetic gap 7sandwiched between the magnetic layers 2 a and 2 b.

Let us put that a magnetic gap depth is D, a magnetic gap length is g,the inner circumferential length (length of the line A-B-C-D) of amagnetic core, which consists of the magnetic layers 1 a, 2 a and 2 band surrounds the coil 4 is Lc, an average magnetic flux density (unit:T (tesla)) necessary to generate a predetermined recording magneticfield needed to magnetize a magnetic recording medium is Bav, and theeffective magnetic permeability of the ring-shaped magnetic core is μ,as shown in FIG. 3.

As described above, the thin-film magnetic head shown in FIG. 3 are notconstituted of a coil having a circular cross section and a cylindricalmagnetic core concentrically surrounding this coil. By considering themagnetic core of this thin-film magnetic head as a cylindrical magneticcore, however, the recording magnetomotive force I can be calculatedapproximately. That is, if the circumferential length Lc and themagnetic gap depth D are considered as Lc=2π Rin and D=Rout−Rin whereRout and Rin are variables in the equation (7), the magnetomotive forceI can be expressed as follows:$I = \frac{2\pi \quad {DBav}}{{\mu Log}\{ { \lbrack {( {{Lc} + g} ) + {2\pi \quad D}}  )/( {{Lc} + g} )} \}}$

where Log is a natural logarithm and variables in this equation areexpressed in SI units.

By determining Lc, g and D in such a manner that the recordingmagnetomotive force I expressed by this equation becomes 0.001 A·T to0.1 A·T, it is possible to magnetize a magnetic recording medium withmagnetomotive force considerably lower than that of the conventionalring-shaped inductive magnetic head. It is therefore possible to easilyaccomplish the reduction in number of the coil turns (including a singleturn) and miniaturize the magnetic core with high reliability. Thisdesign also facilitates the head fabrication and improves the productionyield. It is also possible to form a magnetic core with a narrow trackwidth of several μm or below and accomplish high working precision.

For example, with Lc=5 μm, D=0.5 μm, μ (as the specific magneticpermeability)=200 and Bav=1 T, the value of the magnetomotive force Ineeded to magnetize a magnetic recording medium will be 26 mA·T, whichis very low. Therefore, this level of magnetomotive force can be wellachieved by a single coil turn, which provides a recording current of 26mA.

This means that the conventional recording driver circuit can be used,and because of the current being equal to or smaller than that of theconventional head, there hardly is a need to concern the deteriorationof the reliability originating from the heat generated by the coil.Further, the single-turn design will significantly reduce the inductanceof the coil (which is proportional to a square of the number of coilturns), thus ensuring significant widening of the recording frequencyband.

Since the thicknesses of the magnetic layers 2 a and 2 b constitutingthe magnetic core which is located on the side of the medium opposingface 8 are D (=0.5 μm), the existing semiconductor process technologycan be used to design the track width with the allowance of about ±0.05μm as has already been discussed. This facilitates the fabrication of athin-film magnetic head that ensures a very narrow track of 1 μm orbelow. Furthermore, due to the simple head structure, the productionyield is very high.

As long as Lc, D and g are determined using the above-given equation,the other factors, such as the size and shape of the magnetic core, maybe changed freely. For instance, the thickness of the magnetic layer 1 aand those of the magnetic layers 2 a and 2 b at a given distance awayfrom the magnetic gap portion may be set larger than the magnetic gapdepth D. This improves the effective magnetic permeability μ of themagnetic core and can thus ensure recording with lower magnetomotiveforce.

Embodiment 2

FIG. 4 is a cross section showing a thin-film magnetic head according tothe second embodiment of this invention. This thin-film magnetic head isa ring-shaped thin-film magnetic head, which comprises a lower magneticpole 1, an insulating layer 3, a coil 4, an upper magnetic pole 2 and ahead protective layer 5 laminated in order on a head substrate 6, with amagnetic gap 7 sandwiched between the lower magnetic pole 1 and theupper magnetic pole 2.

Given that a magnetic gap length is g, a magnetic gap depth is D, thethickness of the lower magnetic pole 1 on the medium opposing face 8 isP1, the thickness of the upper magnetic pole 2 on the medium opposingface 8 is P2, the inner circumferential length (length of the lineA-B-C) of the magnetic core, which consists of the lower magnetic pole 1and the upper magnetic pole 2 and surrounds the coil 4 is Lc, an averagemagnetic flux density (unit: T (tesla)) necessary to generate apredetermined recording magnetic field needed to magnetize a magneticrecording medium is Bav, and the effective magnetic permeability of thering-shaped magnetic core is μ, as shown in FIG. 4, the same advantagesas those of the first embodiment can be obtained by the same action ofthe first embodiment if Lc, g, D, P1 and P2 are determined in such amanner that the magnetomotive force I, expressed by the followingequation based on the above-given equation (7) as in the firstembodiment, becomes 0.001 A·T to 0.1 A·T, preferably 0.07 A·T or less.$I = \frac{2\pi \quad {DBav}}{{\mu Log}\{ { \lbrack {( {{Lc} + g} ) + {2\pi \quad D}}  )/( {{Lc} + g} )} \}}$

and

P1≅P2≅D

where Log is a natural logarithm, and variables in this equation areexpressed in SI units.

As long as the above equation is satisfied in this example too, thethicknesses of the lower magnetic pole 1 and the upper magnetic pole 2at a given distance away from the medium opposing face may be set largerthan the magnetic gap depth D. This increases the effective magneticpermeability μ of the magnetic core more than the structure having boththe lower magnetic pole 1 and the upper magnetic pole 2 designed to havethe same thickness D (P1≅P2), thus ensuring further reduction of themagnetomotive force.

With P1≅P2≅D≦0.5 μm, it is easy to form a magnetic core having a trackwidth of 1 μm or narrower.

Embodiment 3

FIG. 5 is a cross section showing a perpendicular thin-film magnetichead according to the third embodiment of this invention. Thisperpendicular thin-film magnetic head performs recording andreproduction when in use with a perpendicular double-layered magneticrecording medium 13, which has a highly permeable layer 12 and aperpendicular recording layer 11 laminated in this order on a mediumsubstrate 14.

This perpendicular thin-film magnetic head comprises a magnetic corehaving a main magnetic pole 9 and a highly permeable return path 10,which is magnetically coupled to this main magnetic pole 9, and a coil 4which is surrounded by the magnetic core through an insulating layer 3.

Given that the inner circumferential length (length of the line A-B-C-D)of the magnetic core surrounding the coil 4 is Lc, the distance from themedium opposing face 8 of the perpendicular thin-film magnetic head tothe recording-layer side face of the highly permeable layer 12 of theperpendicular double-layered medium 13 is S, the interval between themain magnetic pole 9 and the return path 10 at the position of themedium opposing face 8 is Lb, the film thickness in the vicinity of themedium opposing face 8 of the main magnetic pole 9 is Tm, an averagevalue of the density of a magnetic flux (unit: T (tesla)) generatedtoward the highly permeable layer 12 from the distal end portion of themain magnetic pole 9, needed for sufficiently magnetizing theperpendicular recording layer 11, is Bav and the effective magneticpermeability of the magnetic core is μ (μ is a value when the highlypermeable layer 12 is considered to be included in the magnetic core),with the highly permealbe layer 12 considered as a part of the magneticcore, the writing magnetomotive force I can be approximately expressedby the following equation based on the equation (7) as per the first andsecond embodiments.

By determining Lc, S, Lb and Tm (equivalent to D in the firstembodiment) in such a manner that the magnetomotive force I becomes0.001 A·T to 0.1 A·T, preferably 0.07 A·T or less, the same advantagesas those of the first embodiment can be obtained by the same action ofthe first embodiment.$I = \frac{2\pi \quad {TmBav}}{{\mu Log}\{ {( {L + {2\pi \quad {Tm}}} )/L} \}}$

where L=Lc+2S+Lb and L means the inner circumferential length of themagnetic core surrounding the coil 4 when the highly permeable layer 12is considered as a part of the magnetic core. The variables in thisequation are expressed in SI units.

As long as the above equation is satisfied in this example too, thethickness of the main magnetic pole 9 at a given distance away from thereturn path 10 and the medium opposing face 8 may be set larger than Tm.This increases the effective magnetic permeability μ of the wholemagnetic core more than the structure which has the main magnetic pole 9and the return path 10 designed to have the same thickness Tm, thusensuring further reduction of the magnetomotive force.

Embodiment 4

FIG. 6 is a cross section showing a perpendicular thin-film magnetichead of a horizontal type according to the fourth embodiment of thisinvention. This thin-film magnetic head comprises a highly permeablereturn path 10, an insulating layer 3, a coil 4, a main magnetic pole 9,and a protective layer 5 laminated in order on a head substrate 6. Giventhat the inner circumferential length (length of the line A-B-C-D) ofthe magnetic core, which consists of the main magnetic pole surroundingthe coil 4 and the return path 10, is Lc, the distance from the mediumopposing face 8 of the thin-film magnetic head to the recording-layerside face of the highly permeable layer 12 of the perpendiculardouble-layered medium 13 is S, the interval between the main magneticpole 9 and the return path 10 at the position of the medium opposingface 8 is Lb, the film thickness in the vicinity of the medium opposingface 8 of the main magnetic pole 9 is Tm, an average value of thedensity of a magnetic flux (unit: T (tesla)) generated toward the highlypermeable layer 12 from the distal end portion of the main magnetic pole9, needed for sufficiently magnetizing the perpendicular recording layer11, is Bav and the effective magnetic permeability of the magnetic coreis μ (supposing that the highly permeable layer 12 is included in themagnetic core), the recording magnetomotive force I can be approximatelyexpressed in the same form as in the third embodiment.

By determining Lc, S, Lb and Tm in such a manner that the magnetomotiveforce I becomes 0.001 A·T to than 0.1 A·T, preferably 0.07 A·T or less,the same advantages as those of the first to third embodiments can beobtained by the same action of those embodiments. Further, theperpendicular thin-film magnetic head according to this embodiment hasan advantage over the perpendicular thin-film magnetic head of the thirdembodiment in the head fabrication process such that it will ensurefurther miniaturization of the magnetic core and lower magnetomotiveforce.

Embodiment 5

FIG. 7 is a cross section showing a thin-film magnetic head according tothe fifth embodiment of this invention. This thin-film magnetic head hasthe same structure as the thin-film magnetic head of the firstembodiment shown in FIG. 3 except that this thin-film magnetic head hasa thin film 15 provided at the interface between the magnetic layer 1 aand the magnetic layer 2 a and the interface between the magnetic layerla and the magnetic layer 2 b. The thin film 15 is made of at least onetype of magnetic or non-magnetic material selected from a group of anon-magnetic material, a magnetic material having a lower saturationmagnetic flux density than those of the magnetic layers 1 a and 2 a, andan antiferromagnetic material.

The thin film 15 is very thin, on the order of several tens ofangstroms. The material for the thin film 15 may be a Permalloy alloy,Co-based amorphous material, Fe-based soft magnetic material or Co-basedmagnetic material.

This thin-film magnetic head has the following advantages besides thesame advantages as the thin-film magnetic head of the first embodimentshown in FIG. 3. The provision of the thin film 15 can weaken or cut offthe exchange coupling at the interface between the magnetic layers 1 aand 2 a and the magnetic layers 1 a and 2 b. Further, the magneticresistance of the thin film 15 itself is as low as value as can benegligible as compared with the magnetic resistance of the wholering-shaped magnetic core. Even if the size of the ring-shaped core isreduced in accordance with the reduction in magnetomotive force,therefore, the spatial deformation of the signal magnetizationdistribution in the magnetic core, caused by the attraction of thesignal magnetic flux from the magnetic recording medium by the magneticcore can be reduced, thus preventing the averaged magnetic permeabilityof the magnetic core from decreasing. This means that lowermagnetomotive force can easily be accomplished without decreasing theefficiency of the magnetic core when the magnetic core is miniaturized.Particularly, when an antiferromagnetic material is used for the thinfilm 15, in addition to those advantages, single domain formation in thewhole magnetic core is possible so that various magnetic noisesgenerated at the time of recording can be reduced, thus ensuringhigh-quality recording.

Embodiment 6

FIG. 8 is a cross section showing a thin-film magnetic head according tothe sixth embodiment of this invention. This thin-film magnetic head hasthe same structure as the thin-film magnetic head of the secondembodiment shown in FIG. 3 except that this thin-film magnetic head hasa thin film 15 provided at the interface 16 between the lower magneticpole 1 and the upper magnetic pole 2. The thin film 15 is made of atleast one type of magnetic or non-magnetic material selected from agroup of a non-magnetic material, a magnetic material having a lowersaturation magnetic flux density than those of the lower magnetic pole 1and the upper magnetic pole 2, and an antiferromagnetic material. Thethickness of and the material for the thin film 15 are the same as thoseof the fifth embodiment.

This thin-film magnetic head has the same advantages as the thin-filmmagnetic head of the second embodiment shown in FIG. 4, as well as thesame action and advantages as the thin-film magnetic head of the fifthembodiment due to the provision of the thin film 15.

Embodiment 7

FIG. 9 is a cross section showing a perpendicular thin-film magnetichead according to the seventh embodiment of this invention. Thisperpendicular thin-film magnetic head has the same structure as thethin-film magnetic head of the third embodiment shown in FIG. 5 exceptthat this thin-film magnetic head has a thin film 15 provided at theinterface between the main magnetic pole 9 and the return path 10. Thethin film 15 is made of at least one type of magnetic or godnon-magnetic material selected from a group of a non-magnetic material,a magnetic material having a lower saturation magnetic flux density thanthose of the main magnetic pole 9 and the return path 10, and anantiferromagnetic material. The thickness of and the material for thethin film 15 are the same as those of the fifth embodiment.

This thin-film magnetic head has the same advantages as the thin-filmmagnetic head of the third embodiment shown in FIG. 5, as well as thesame action and advantages as the thin-film magnetic head of the fifthembodiment due to the provision of the thin film 15.

Embodiment 8

FIG. 10 is a cross section showing a horizontal type perpendicularthin-film magnetic head according to the eighth embodiment of thisinvention. This horizontal type perpendicular thin-film magnetic headhas the same structure as the thin-film magnetic head of the fourthembodiment shown in FIG. 6 except that this thin-film magnetic head hasa thin film 15 provided at the interface between the main magnetic pole9 and the return path 10. The thin film 15 is made of at least one typeof magnetic or non-magnetic material selected from a group of anon-magnetic material, a magnetic material having a lower saturationmagnetic flux density than those of the main magnetic pole 9 and thereturn path 10, and an antiferromagnetic material. The thickness of andthe material for the thin film 15 are the same as those of the fifthembodiment.

This thin-film magnetic head has the same advantages as the thin-filmmagnetic head of the third embodiment shown in FIG. 5, as well as thesame action and advantages as the thin-film magnetic head of the fifthembodiment due to the provision of the thin film 15.

This thin-film magnetic head has the same advantages as the thin-filmmagnetic head of the fourth embodiment shown in FIG. 6, as well as thesame action and advantages as the thin-film magnetic head of the fifthembodiment due to the provision of the thin film 15 because of theprovision of the non-magnetic layer 15, or the magnetic layer 15 havinga lower saturation magnetic flux density than those of the magneticlayers 1 a, 2 a and 2 b, or the antiferromagnetic layer 15.

Embodiment 9

In a combination of a thin-film magnetic head, which comprises aring-shaped magnetic core made of Permalloy and a one-turn coil woundaround the magnetic core and a longitudinal recording medium of aCoPt-based material, the parameters are set as follows:

inner circumferential length of the Lc: 5 μm magnetic core surroundingthe coil magnetic gap length g: 0.2 μm magnetic gap depth D: 0.24 μmsaturation magntic flux density Bs: 1 T of the magnetic core effectivespecific magnetic μ: 300 permeability of the magnetic core spacingbetween the head and medium d: 0.03 μm thickness of longitudinal δ: 0.03μm recording layer coercive force of the medium Hc: 159000 A/m (= 2000Oe)

the magnetomotive force I needed to generate the average magnetic fluxdensity Bav nearly equal to the saturation magnetic flux density Bs ofthe magnetic core in the magnetic gap when the recording current issupplied to the coil, is computed to be 15.7 mA·T (<0.1 A·T) from theequation (1). At this time, the intensity of the recording magneticfield in the longitudinal direction of the recording track at the pointP on the bottom surface of the longitudinal recording layer directlybelow the magnetic gap is obtained to be 361,000 A/m (=4530 Oe) from theequation (3). It is apparent that this intensity is sufficient to makerecording on the recording medium with the aforementioned coerciveforce. As apparent from the above, recording can be made on a recordingmedium having high coercive force, with sufficiently low magnetomotiveforce, as compared with the prior art.

Embodiment 10

In a combination of a perpendicular thin-film magnetic head, whichcomprises a magnetic core having a main magnetic pole made of Permalloy,a return path of a high magnetic permeability to be magnetically coupledto is the main magnetic pole, and a coil surrounded by the magneticcore, and a perpendicular double-layered magnetic recording mediumhaving a highly permeable layer and a perpendicular recording layerlaminated on a substrate in the named order, with the parameters set asfollows:

inner circumferential length of the Lc: 5 μm magnetic core surroundingthe coil spacing between the main magnetic d: 0.03 μm pole andperpendicular recording layer thickness of the perpendicular δ: 0.05 μmrecording layer distance between the main magnetic pole S: 0.08 μm andthe perpendicular recording layer (= d + δ) interval between the mainmagnetic Lb: 2 μm pole and return path at the position of the mediumopposing face film thickness in the vicinity of Tm: 0.2 μm the mediumopposing face of the main magnetic pole saturation magnetic flux densityBs: 1 T of the main magnetic pole effective specific magnetic μ: 300permeability of the magnetic core spacing between the head and medium d:0.03 μm thickness of perpendicular δ: 0.05 μm recording layer thicknessof perpendicular recording layer coercive force of the medium Hc: 159000A/m (= 2000 Oe)

the magnetomotive force I needed to provide the average magnetic fluxdensity Bav nearly equal to the saturation magnetic flux density Bs ofthe main magnetic pole between the main magnetic pole and theperpendicular recording layer when the recording current is supplied tothe coil, is computed to be 20.6 mA·T (<0.1 A·T) from the equation (2).At this time, the intensity of the recording magnetic field in theperpendicular direction to the recording surface at the point P on thebottom surface of the longitudinal recording layer directly below themain magnetic pole is obtained to be 446,00 A/m (=5600 Oe) from theequation (3). It is apparent that this intensity is sufficient to makerecording on the recording medium with the aforementioned coerciveforce. As apparent from the above, recording can be made on a recordingmedium having high coercive force, with sufficiently low magnetomotiveforce, as compared with the prior art.

Although ten embodiments have been described herein, it should beapparent to those skilled in the art that this invention may be embodiedin various other specific forms given below.

(1) The coil may be made of a high melting-point metal. Tungsten ormolybdenum may be used as the high melting-point metal. Theminiaturization of the magnetic head increases the density of thecurrent flowing across the coil, and causes electromigration and heatgeneration, so that the coil is easily cut. This problem can however beovercome by the use of a high melting-point metal for the coil. Thesurface of the coil made of a high melting-point metal may be oxidized,forming an oxide film of a high melting-point metal. This allows asmooth magnetic path to be formed. Further, the high melting-point metalcoil and the oxide film on the surface of that coil can providemagnetostatic coupling between the upper magnetic layer and the lowermagnetic layer, so that the magnetic permeability can be maintained eventhough fine patterning.

(2) The provision of an antiferromagnetic film 16 at the position asshown in FIGS. 11A to 11C permits the magnetic pole to be securelymagnetized, thus reducing noise.

(3) A dummy projection may be provided at the peripheral portion of aprotruding to-be-polished surface at the time of polishing the slidingsurface of the magnetic head to increase the area of the to-be-polishedportion, thereby improving the depth accuracy.

As described above, this invention has the following advantages.

(1) Since the magnetomotive force can be made significantly lower thanthat of the conventional head, it is easy to design the coil to havefewer turns, particularly, a single turn. This design simplifies thefabrication process and is excellent in mass production.

(2) As the head becomes very small as compared with the conventionalhead, a multi-channel structure becomes easier.

(3) Due to the fewer turns, the impedance of the head is reducedconsiderably. The rising time and falling time of the recording currentbecome shorter, thus widening the recording frequency band accordingly.

(4) As the magnetomotive force and the impedance are reducedconsiderably, the power needed for recording can also be reducedsignificantly, thereby overcome the problem of the recording-currentoriginated heat generation at the head portion. The reliability of thehead is thus improved.

(5) Due to the head size considerably smaller than that of theconventional head, the thickness of the magnetic pole becomes on thesub-micron order (micron order in the prior art), so that the workingprecision in the thin-film etching process for the track width or thelike is significantly improved and the fabrication of a thin-filmmagnetic head having a very narrow track width of 1 μm or below becomessignificantly easy.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details, and representative devices, shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A thin-film magnetic head comprising aring-shaped magnetic core and a coil surrounded by said magnetic core,said magnetic core forming part of a magnetic path, given that an innercircumferential length of said magnetic core surrounding said coil isLc, a magnetic gap length is g, a magnetic gap depth is D, an averagemagnetic flux density (unit: T (tesla)) is Bav and an effective magneticpermeability of said magnetic core is μ, wherein Lc, g and D aredetermined such that a magnetomotive force I needed for recording,expressed by a following equation (1), is in a range of 0.001 A·T to 0.1A·T. (Ampere·Turn): $\begin{matrix}{I = \frac{2\pi \quad {DBav}}{{\mu Log}\{ {( {( {{Lc} + g} ) + {2\pi \quad D}} )/( {{Lc} + g} )} \}}} & \text{(1)}\end{matrix}$

wherein Log is a natural logarithm, and variables in said equation (1)are expressed in SI units; and wherein said magnetic core comprises afirst magnetic layer formed on a head substrate side and a secondmagnetic layer formed on said first magnetic layer, with a thin film ora multi-layered thin film provided in a part of said magnetic path,which cuts said magnetic path and is an interface between said firstmagnetic layer and said second magnetic layer exclusive of the magneticgap, said thin film or multi-layered thin film being made of at leastone type of magnetic or non-magnetic material selected from the group ofa non-magnetic material, a magnetic material having a lower saturationmagnetic flux density than that of said magnetic core, and anantiferromagnetic material.
 2. The thin-film magnetic head according toclaim 1, wherein Lc, g and D are determined such that said magnetomotiveforce I ranges from 0.001 A·T to 0.07 A·T.
 3. The thin-film magnetichead according to claim 1, wherein Lc, g and D are determined such thatsaid magnetomotive force I ranges from 0.01 A·T to 0.07 A·T.
 4. Thethin-film magnetic head according to claim 1, wherein D is in a range of0.1 μm to 0.5 μm.
 5. The thin-film magnetic head according to claim 1,wherein said non-magnetic material is selected from the group consistingof Al₂O₃, SiO₂ and Cu, said magnetic material having a lower saturationmagnetic flux density than that of said magnetic core is selected fromthe group consisting of CoZr-based amorphous material and NiFecontaining Nb or Rh, and said antiferromagnetic material is selectedfrom the group consisting of FeMn, NiO and PtMn.
 6. A magneticwrite/read apparatus equipped with a recording magnetic head comprisinga ring-shaped magnetic core and a coil surrounded by said magnetic core,said magnetic core forming part of a magnetic path, and a magneticrecording medium on which recording is done by said recording magnetichead, given that an inner circumferential length of said magnetic coresurrounding said coil of said recording magnetic head is Lc, a magneticgap length is g, a magnetic gap depth is D, an average magnetic fluxdensity (unit: T (tesla)) is Bav and an effective magnetic permeabilityof said magnetic core is μ, wherein Lc, g and D are determined such thata magnetomotive force I needed for recording, is expressed by afollowing equation (1), $\begin{matrix}{I = \frac{2\pi \quad {DBav}}{{\mu Log}\{ {\lbrack {( {{Lc} + g} ) + {2\pi \quad D}} \rbrack/( {{Lc} + g} )} \}}} & \text{(1)}\end{matrix}$

where Log is a natural logarithm, and variables in said equation (1) areexpressed in SI units, and I is in the range of 0.001 A·T to 0.1 A·T(Ampere·Turn), and a magnetic field intensity Hx in a magnetic-headrunning direction of said magnetic recording medium immediately below acenter portion of the magnetic gap of said recording magnetic head isexpressed by a following equation (2) and said magnetic field intensityHx and coercive force Hc of said magnetic recording medium having arelation of Hx>Hc: $\begin{matrix}{{Hx} = {\frac{2{Bs}}{{\pi\mu}_{0}}\{ {{\tan^{- 1}\quad \frac{t_{w}( {D + d + \delta} )}{g\sqrt{( {t_{w}/2} )^{2} + ( {d + \delta} )^{2} + ( {g/2} )^{2}}}} - {\tan^{- 1}\quad \frac{t_{w}( {d + \delta} )}{g\sqrt{( {t_{w}/2} )^{2} + ( {d + \delta} )^{2} + ( {g/2} )^{2}}}}} \}}} & (2)\end{matrix}$

wherein t_(w) is a track width, Bs is a saturation magnetic flux density(unit: T (tesla)) of a magnetic head core necessary to generate arecording magnetic field needed for magnetization of said magneticrecording medium, μ_(O) is a magnetic permeability in vacuum, d isspacing between said recording magnetic head and said magnetic recordingmedium, and δ is a thickness of a recording layer of said magneticrecording medium, and where variables in said equation (2) are expressedin SI units.
 7. The magnetic write/read apparatus according to claim 6,wherein Lc, g and D are determined such that said magnetomotive force Iranges from 0.001 A·T to 0.07 A·T.
 8. The magnetic write/read apparatusaccording to claim 6, wherein Lc, g and D are determined such that saidmagnetomotive force I ranges from 0.01 A·T to 0.07 A·T.
 9. The magneticwrite/read apparatus according to claim 6, wherein D is in a range of0.1 μm to 0.5 μm.
 10. The magnetic write/read apparatus according toclaim 6, wherein said magnetic core comprises a first magnetic layerformed on a head substrate side and a second magnetic layer formed onsaid first magnetic layer, with a thin film or a multi-layered thin filmprovided in a part of said magnetic path, which cuts said magnetic pathand is an interface between said first magnetic layer and said secondmagnetic layer exclusive of the magnetic gap, said thin film ormulti-layered thin film being made of at least one type of magnetic ornon-magnetic material selected from the group of a non-magneticmaterial, a magnetic material having a lower saturation magnetic fluxdensity than that of said magnetic core, and an antiferromagneticmaterial.
 11. The magnetic write/read apparatus according to claim 10wherein said non-magnetic material is selected from the group consistingof Al₂O₃, SiO₂ and Cu, said magnetic material having a lower saturationmagnetic flux density than that of said magnetic core is selected fromthe group consisting of CoZr-based series amorphous material and NiFecontaining Nb or Rh, and said antiferromagnetic material is selectedfrom the group consisting of FeMn, NiO and PtMn.